(2)
The fuel strainer housing contains a line replaceable fuel strainer, an inlet and outlet port, poppet check valves (to stop fuel flow with the fuel strainer removed for maintenance) and a cap for access to the fuel strainer.
(3)
When the fuel strainer is removed from the fuel strainer housing, the maximum quantity of fuel that can drain from the fuel strainer is 15 cubic inches (245 cubic centimeters) of fuel. With the fuel strainer and cap removed, the maximum rate of the leakage is 0.06 cubic inch (1 cubic centimeter) per minute at any fuel system pressure.
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(4) With the strainer removed and the cap replaced, fuel cannot go through the fuel strainer housing through the inlet or the outlet ports at any fuel system pressure.
NOTE: There is not a fuel strainer bypass function.
____
E. Fuel Strainer
(1)
There is a fuel strainer in each of the fuel strainer assemblies located on the rear spar of the center wing tank (Ref LBL/RBL 112.60). To get to the fuel strainers you must go in the wheel well for the wing landing gear and remove the cap from the fuel strainer assembly.
(2)
The fuel strainer does not let unwanted particles to go through the fuel strainer housing and into the fuel scavenge system. The fuel strainer will stop a 0.025 inch diameter particle.
(3)
The fuel strainer can be cleaned with water or shop air pressure (up to 90 PSI).
F.
Operation (Fig. 1)
(1)
Functional Description
(a)
The fuel scavenge system operates when the fuel-feed transfer line is pressurized by one or more of the boost pumps or the override/jettison pumps. A fuel line in the center wing tank connects the fuel-feed transfer line to the scavenge system.
(b)
Fuel flows from the pressurized fuel-feed transfer line to the inlet port of the fuel strainer housing. Check valves in the fuel strainer housing prevents the flow of fuel from the scavenge system back into the fuel-feed transfer line (reverse flow). The fuel then flows into the motive flow lines through the outlet port of the fuel strainer housing.
(c)
With the center wing tank full, the float valves in the center wing tank are closed. As the fuel level in the center wing tank decreases (to approximately 4000 lbs/1820 kgs), the float valves open and fuel flows from the motive lines and into the jet pumps. The float valves in the center wing tank are located approximately 2 inches above the center wing tank pump inlets.
(d)
The jet pumps use the fuel flow from motive lines to supply the motive port with fuel pressure. The motive port pulls a secondary fuel flow from the fuel inlet on the bottom of the center wing tank through the jet pump induced port. The motive and induced flow are mixed together and then exit the jet pump through the discharge port. The fuel flows through a tube attached to the wing center section mid spar into the No. 2 or the No. 3 main tank. A check ball in the jet pump closes when the motive flow pressure is low to stop the flow of fuel back into the center wing tank.
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28-15-00
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747-400
MAINTENANCE MANUAL
(e)
With the inboard main tanks full, the float valves in the inboard main tanks are closed. The closed float valves prevent the flow of fuel from the scavenge system into the inboard main tanks when the inboard main tanks are full. The closed float valves also prevent the flow of fuel from the inboard main tanks back into the center wing tank (reverse flow).
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